This invention relates to touch panels and to electronic displays.
Flat panel displays are typically backlit by light guide slabs (often referred to as xe2x80x9cbacklightsxe2x80x9d) that provide uniform illumination to a transmissive light valve. The backlight may be the primary light source for the display, or a source of supplemental illumination in a predominantly reflective (often referred to as a xe2x80x9ctransflectivexe2x80x9d) display. Alternatively, flat panel reflective displays may be front-lit by a light guide slab (often referred to as a xe2x80x9cfrontlightxe2x80x9d or xe2x80x9cfront light guidexe2x80x9d) that provides uniform illumination from the viewing side of a reflective light valve. This allows elimination of the backlight and placement of a reflector in the light valve, thereby increasing the display""s reflectivity and brightness in well-lit ambient light conditions when the frontlight is turned off. Front light guides should have sufficient clarity so that they do not distort or significantly attenuate the display image. Preferably the front light guide also uniformly illuminates the display at a brightness level sufficient to render the display readable in dark ambient conditions.
Displays may also incorporate touch panels that allow the user to input information via a stylus or finger pressure. For example, a common type of touch panel known as a xe2x80x9cresistive overlayxe2x80x9d design utilizes two transparent layers with partially conductive coatings separated by spacers. When the layers are pressed together, the electrical resistance is sensed in two dimensions to obtain the coordinates of the contact point. The bottom layer (the layer closest to the display) typically is quite stiff and made of glass. The top layer (the layer that will be touched by the stylus or finger) typically is fairly flexible and made of plastic.
Resistive overlay and other touch panel designs are described in the xe2x80x9cCarroll Touch Handbookxe2x80x9d, available at www.carrolltouch.com. Many such other touch panel designs, including xe2x80x9ccapacitive overlayxe2x80x9d, xe2x80x9cguided acoustic wavexe2x80x9d, xe2x80x9csurface acoustic wavexe2x80x9d and xe2x80x9cnear field imagingxe2x80x9d (see U.S. Pat. No. 5,650,597) touch panels, incorporate an optically clear, relatively stiff slab atop the display. Some types of xe2x80x9cscanning infraredxe2x80x9d touch panels also incorporate an optically clear, relatively stiff slab atop the display. As with resistive overlay designs, glass is most commonly used to form the stiff slab.
Japanese Published Patent Application No. JP 11344695A (equivalent to WO 9963394) shows an integral front light guide and touch panel in which the light guide portion is made of molded plastic. The upper surface of the light guide is bonded to the lower surface of the touch panel using a layer of transparent resin, and the lower surface of the light guide has a polygonal or circular dot pattern formed by an ink of transparent or semi-transparent resin having a higher refractive index than the light transmission plate and containing a photodiffusion pigment. Alternatively, the lower surface of the light guide can be formed with xe2x80x9cfine crimpsxe2x80x9d or with xe2x80x9cprismsxe2x80x9d (shown as sawtooth projections) formed parallel to the end face of the input of the light transmission plate. The light guide of this reference utilizes scattering by the above-mentioned photodiffusion pigment, or refraction through the above-mentioned crimps or prisms, to extract light from the light guide into a light valve. The sawtooth projections in this reference are oriented with the inclined portion of the sawtooth facing away from the light input end of the light guide.
Japanese Published Patent Application No. JP 2000-47178A shows an integral front light guide and touch panel in which the light guide portion is wedge-shaped and has a pattern of spacers on its upper surface. The light guide of this reference utilizes scattering by the spacers to extract light from the light guide into a light valve.
Other illuminated touch panel display devices are shown in Japanese Published Patent Application Nos. JP 61188515A, JP 11065764A, JP 11110131A, JP 11174972A, JP 11260133A, JP 11316553A, JP 11065764A and JP 2000075293A, and in PCT Published Patent Application No. WO 99/63394A.
U.S. Pat. No. 5,396,350 shows a backlight having an array of microprisms that reflect light into a transmissive light valve.
U.S. Pat. No. 5,428,468 shows an illumination system employing a waveguide and an array of microprisms that reflect light out of the waveguide. U.S. Pat. No. 5,995,690 shows a light extraction tape for coupling light out of a waveguide.
Other illuminated frontlit or backlit illumination or display devices are shown in U.S. Pat. Nos. 4,373,282; 4,528,617; 4,751,615; 4,799,137; 4,811,507; 4,874,228; 5,005,108; 5,050,946; 5,054,885; 5,190,370; 5,341,231; 5,359,691; 5,485,354; 5,506,929; 5,555,109; 5,555,329; 5,575,549; 5,594,830; 5,608,550; 5,608,837; 5,613,751; 5,668,913; 5,671,994; 5,835,661; 5,894,539; 6,011,602 and 6,139,163; and in European Patent Application EP 0 802 446 A1.
Typically, touch panel fabrication requires one or more manufacturing steps that involve high temperatures or other harsh processing conditions. For example, many touch panel designs employ a conductive or capacitive layer of indium tin oxide (xe2x80x9cITOxe2x80x9d). The processing temperatures required to apply a satisfactory ITO layer will destroy most plastic substrates. The touch panel also should have good optical properties. Thus the touch panel often includes a heat-resistant glass substrate that can support an ITO layer or other heat-processable layers of the touch panel. Such touch panels can be combined with a separate front light guide, which should also have good optical properties, including good light extraction characteristics. The front light guide can be made, for example, from a molded plastic wedge, and the resulting combination placed atop a reflective light valve. This approach employs extra parts, has an extra interface in the supplied light path, and has increased overall thickness. However, such an approach also permits the lower slab of the touch panel to be fabricated from flat glass, which is relatively low in cost and can survive the processing steps required to form a layer of ITO or other applied material.
Although a number of illuminated touch panel devices have been proposed, there is an ongoing need for thinner, more efficient or more evenly illuminated devices, for devices that could be more easily constructed, and for devices with reduced power consumption. Many current devices do not use all of the light supplied by the light source. If such unused light could be channeled to the display, then power consumption could be further reduced and display brightness could be increased.
Some of the above-mentioned illuminated touch panel devices employ scattering or refraction to extract light from the light guide. These approaches can cause reduction in contrast, or can supply light at less than optimal angles to a light valve in the display.
The present invention provides, in one aspect, a frontlit touch panel for use with a reflective light valve, comprising a front light guide having at least one light input face that supplies light to the guide, a viewing face, a light output face opposite the viewing face, and at least one component of a touch-sensitive transducer, the light output face having a light extraction layer thereon having a substantially flat light exit face and containing buried reflective facets that extract supplied light from the guide through the light exit face. The touch panel can be easily fabricated, for example, by fabricating a component (e.g., a conductive or capacitive layer) of a touch-sensitive transducer on an ordinary flat glass sheet, and by laminating the resulting assembly to a plastic extraction film. An optional top membrane can be applied atop the touch panel, and an optional antireflection coating can be applied to the light exit face of the structured-surface film.
The present invention also provides an illuminated touch panel display comprising:
a) at least one light source;
b) a front light guide having at least one light input face through which light from the source can be supplied to the guide, a viewing face, a light output face opposite the viewing face, and at least one component of a touch-sensitive transducer, the light output face having a light extraction layer thereon having a substantially flat light exit face and containing buried reflective facets that extract supplied light from the guide through the light exit face; and
c) a reflective light valve that receives extracted light from the guide and returns at least some of that light through the viewing face.
Compared to the use of a separate touch panel and front light guide, the frontlit touch panels of the invention can have reduced overall thickness, higher transmission and fewer interfaces. The panels can be fabricated using ordinary flat glass and existing touch panel manufacturing methods and equipment to provide a touch panel having added functionality. Preferably the frontlit touch panels of the invention have a composite construction comprising a layer of glass and one or more other layers made of different materials (e.g., conductive layers, solder traces, sensors or other touch-sensitive-transducer-related components on one major face of the touch panel, and a microstructured plastic surface and optional antireflection coating on the other major face of the touch panel). Preferred embodiments of the panels efficiently extract supplied light while exhibiting good contrast and low distortion. Because the frontlit touch panel has microstructured reflective optics located between the touch panel and the light valve and because the touch panel can have a smooth viewing face, the frontlit touch panels of the invention are relatively robust and are less likely to be damaged than touch panels having microstructured optical features on the viewing face.